In order to reduce the nitrogen content of the whole scrap quantum electric arc furnace, optimize the smelting performance of the EAF and reduce the carbon emission of the EAF, the CO₂ injection process was used to replace the original injection process to achieve the above goals. A large number of CO₂ injection process tests were carried out on a 150 t quantum EAF, and the trends of nitrogen content, smelting power consumption, smelting cycle, carbon emission and other performance indexes of the electric arc furnace before and after the improvement process were compared. The test results show that after the CO₂ injection process, the nitrogen mass fraction of the electric arc furnace is reduced by 30.6×10^-6, the smelting power consumption is reduced by 5.6 kWh/t, the smelting cycle is shortened by 3.2 min, the average carbon and oxygen equilibrium is reduced by 4.4×10^-4, the mass fraction of FeO in slag  is reduced by 4.5 %, and the carbon emission is reduced by 8.4 %. By combining the CO₂ carrier gas injection carbon powder process with the Ar+CO₂ dynamic mixed bottom blowing process, it can effectively reduce the nitrogen content of molten steel, smelting power consumption, carbon emissions and other performance indicators, and optimize the quantum electric arc furnace injection process.

KR (Kanbara Reactor) method is the mainstream desulfurization method in hot metal pretreatment. The mixing efficiency of three kinds of blades, namely, the regular four-blade propeller, the spiral three-blade propeller and the double-layer regular four-blade propeller, was studied by numerical simulation method. The results showed that the mixing time of the double-layer regular four-blade propeller was 7.3 % shorter than that of the regular four-blade propeller, and 37.9 % shorter than that of the spiral three-blade propeller. Through the analysis of the axial velocity and turbulent kinetic energy distribution in the molten iron, it was found that the axial velocity of the molten iron in the double-layer regular four-blade propeller agitator was larger, and the turbulent kinetic energy in the molten iron was widely diffused. The average turbulent kinetic energy of double-layer regular four-blade propeller was 28 % greater than that of regular four-blade propeller and 1.8 % greater than that of spiral three-blade propeller.

Based on the actual production data of steelmaking in a 260 t converter, the integrated learning algorithms of RF (Random Forests), LGBM (Light Gradient Boosting Machine) and Stacking integration were used to establish phosphorus and manganese prediction models for blowing endpoint in the converter. The model input variables were determined through the correlation theory analysis and Pearson correlation coefficient method. It was found by comparing the end-point hit rates of the three integrated learning models that the prediction performance of the Stacking integrated model is the best. With error tolerances of the phosphorus mass fraction at the endpoint of blowing being ±0.001 % and ±0.001 5 %, the hit rates are 86.3 % and 97.1 %, respectively. With error tolerances of the end point manganese mass fraction being ±0.008 %, and ±0.01 %, the hit rates are 83.4 % and 94.4 %, respectively.

The direct alloying process of manganese ore was carried out by the process of double slag dephosphorization and less slag smelting. The samples of end-point slag and molten steel were selected for chemical composition and mineral phase detection, and the influence of the optimum ratio of different manganese ores and slag-making materials on the manganese distribution ratio between slag and steel was analyzed. The results show that the manganese yield is 15.87 %-79.3 %, with an average of 45.05 %. The manganese distribution ratio between slag and steel is 21.97-37.96, with an average of 31.17. The dephosphorization rate is 86 %-92 %, with an average of 88 %. The manganese distribution between slag and steel obtained by the charge ratio of group 9, group 4 and group 13 is relatively low, between 22-25. The main factors affecting the distribution ratio of manganese between slag and steel are molten steel temperature, end point carbon content, slag basicity and iron oxide. The quantitative relationship between these factors and the distribution ratio of manganese between slag and steel was obtained.The charge ratio of the low manganese distribution ratio is that the 
proportion of lime is 25 %-30 %, the proportion of sinter is 30 %-40 %, the proportion of manganese ore is 15 %-20 %, and the proportion of light burnt dolomite is 20 %-30 %. 

In order to study the effects of metallurgical properties of slag at the first deslagging on the metallurgical effect of dephosphorization in the converter high-carbon smelting process，the single slag method was used to carry out the industrial test of high efficiency dephosphorization of single slag high draw carbon on a 50 t top-bottom blowing converter in a domestic steel plant. Through theoretical calculation analysis and combined with laboratory research, the relationship between the mineral phase structure, melting temperature, viscosity, composition and other metallurgical properties of the converter slag at the first deslagging and the converter dephosphorization effect was studied. The research results show that the mineral phase structure of Si, Ca and P enriched areas of slag at the first deslagging is mainly 2CaO·SiO₂ and 3CaO·P₂O₅, both of which are favorable to the dephosphorization reaction. The enriched areas of Fe, Mn and Mg elements mainly form RO phase and matrix phase, which are not favorable to the dephosphorization reaction. Reducing the melting temperature and viscosity of the single slagging high carbon tapping of slag at the first deslagging is conducive to the dephosphorization reaction. The melting temperature of slag at the first deslagging is controlled at 1 370-1 375 ℃, the viscosity of slag at the first deslagging is around 0.033 Pa·s, the dephosphorization effect is good, the lowest phosphorus mass fraction of molten steel at the first deslagging is 0.018 %, the phosphorus distribution ratio of slag at the first deslagging is 
greater than 60, the highest dephosphorization rate of the first deslagging is 84 %. Binary basicity R=2.60-3.00, w(FeO)=22.00 %-27.00 %，w(MgO)＜7.50 %，w(MnO)＜4.60 %,slag at the first deslagging has a good dephosphorization effect, the phosphorus distribution ratio of slag at the first deslagging is greater than 60, the dephosphorization rate of the first deslagging is no less than 75 %.

Due to the high inclusion content and low elongation after cold rolling,the DL350 low carbon titanium microalloy cold-rolled structural steel produced by a certain plant cannot meet the customer′s requirements.In order to reduce the production cost and improve the elongation after fracture of cold rolled products,a reasonable slag washing process was developed, and the influence of slag washing process on the cleanliness and performance of steel was analyzed.The results show that the inclusions in steel are mainly MnS, TiN, MnS-TiN and a small amount of Al₂O₃ inclusions, and the content of oxygen and nitrogen in molten steel decreased significantly with slag washing.After slag washing, the average content of micro-inclusions in the billet decreased from 21.3 to 15.7 per mm².At the same time, the grade of Class A inclusion was reduced from 2.0-2.5 to 1.0-1.5, and Class B inclusion was reduced from 1.5-2.0 to 0.5-1.0, indicating that the slag washing process significantly improved the cleanliness of the billet. Through the performance test of hot-rolled and cold-rolled products, it can be found that the elongation after hot-rolled fracture of slag-washing process samples has been increased from 26 %-28 % to 29 %-31 %, and the elongation after cold-rolled fracture has been increased from 15 %-16 % to 18 %-20 %, the overall strength changes little, which meets the customer′s requirements.

In order to explore the formation and evolution mechanism of large-size Al₂O₃-SiO₂-MnO inclusions with the size of more than 10 〖WTBZ〗μ〖WTB4〗m in 37Mn5 steel refining process, the molten steel was systematically sampled during the whole refining process of EAF-LF-VD-calcium treatment-continuous casting for production of 37Mn5 steel. The composition of molte steel was detected, and the morphology and composition characteristics of large-size Al₂O₃-SiO₂-MnO inclusions in different smelting stages were analyzed. Based on actual production process and thermodynamic calculation, the evolution law of this kind of inclusion was revealed. The results show that, due to the low Al content and high O content in local molten steel during EAF tapping process, large-size Al₂O₃-SiO₂-MnO inclusions are formed. At the beginning of LF refining, the local Ca content increases to form Al₂O₃-SiO₂-MnO-CaO inclusions. After the middle stage of LF refining, the Ti content increases to modify the two kinds of inclusions formed at the early stage to form inclusions containing TiOx. With the progress of smelting, the distribution of Ti is gradually uniform in the inclusions. Insufficient calcium treatment after VD results in unsatisfactory modification of inclusions, and has little effect on the large-size inclusions. Reasonable deoxidation, alloying and slagging process can reduce the formation of Al₂O₃-SiO₂-MnO-CaO inclusions, so as to reduce the number of inclusions and improve the quality of steel.

The tundish controlled by induction heating and argon blowing is expected to achieve efficient inclusion removal and low superheat pouring. For the technology, a three-dimensional unsteady mathematical model was established based on the induction heating tundish of a steel mill. The distribution of the magnetic field was studied, and the effects of argon blowing and gas blowing rates on the flow field, temperature field and inclusion removal were compared and analyzed. The results show that the minimum value of eccentric electromagnetic force in the induction heating tundish deviates from the geometric center of the channel by 10 mm, and Joule heat increases slightly along the channel radially closer to the coil. Argon blowing makes the molten steel in the induction heating tundish form a circulating flow on both sides of the gas curtain, eliminating the small inactive circulating flow in the corner of the tundish. And the temperature distribution in the pouring zone is more uniform. Compared with the induction heating tundish without argon blowing, the removal ratio of inclusions after argon blowing increases by 0.4 times, which has better inclusion removal effect. When the gas blowing rate is between 10 and 40 L/min, there is a small circulating flow with low flow rate near the channel side. When the blowing rate is increased to 55 L/min, a stable gas curtain begins to form in the pouring zone, and a circulating flow is formed on both sides of it. In this study, the blowing rate of 55 L/min has the best flow control and inclusion removal effect.

Through solidification simulation calculation and onsite test, the optimal soft reduction process parameters for continuous casting of non quenched and tempered steel were obtained. The No.1-5 reduction rollers perform a reduction of 3 mm-4 mm-5 mm-5 mm-3 mm, corresponding to continuous casting speed of 0.85 m/min,which improves the macro quality, while avoiding the emergence of pressing cracks. Based on the optimal process parameters of soft reduction and casting speed, the influence of electromagnetic stirring on segregation was studied. Combined with the actual equipment, the optimal electromagnetic stirring parameters were obtained through extreme value method experiments, the mould electromagnetic stirring current is 350 A, and the frequency is 2.0 Hz; the final electromagnetic stirring current is 200 A, and the frequency is 6 Hz. Finally, the carbon segregation index in the center of the billet can be controlled to be less than 1.10 by the multivariate coupling study of the process parameters of continuous casting.

In order to reduce the harm of inclusions on the fatigue properties of bearing steel, the modification behavior of inclusions in GCr15 bearing steel by rare earth Ce and heat treatment was studied. It is found that rare earth treatment can spheroidize inclusions in the tested steel and reduce their average size, which is helpful to reduce the hazard of inclusions in aluminum deoxidation bearing steel. Heat treatment (1 250 ℃) can also spheroidize and refine inclusions in the tested steel. With the increase of heat treatment time (0-330 min), the average size, length-width ratio and area fraction of inclusions show a downward trend. Extending the heat treatment time (330-510 min), the proportion of large-size inclusions in aluminum deoxidation bearing steel increases, and the spherical homogeneous Ce-Al-O-S inclusions in rare earth bearing steel transform into Al-rich and Ce-rich heterogeneous inclusions, which is harmful to the fatigue performance of bearing steel. Therefore, when the heat treatment is 330 min, the inclusion characteristics of aluminum deoxidization and rare earth bearing steel are optimal under the conditions of this study.

The cleanliness of battery case steel is an important factor affecting the deep drawing performance. Characterization methods such as metallographic microscopy (OM) and scanning electron microscopy (SEM) were used to sample different parts of the slab and cold rolled plate of a certain factory's battery case steel, and samples of battery cases with sand hole defects were taken to analyze the cleanliness level of battery case steel and identify the causes of quality defects in battery case steel sand holes. The results show that the part which has the largest and densest inclusions in the battery case steel slab is the inner arc 1/4. The part which has the largest size of inclusions in the cold rolled plate is the center, and it also has the lowest density of inclusions. Compared with the battery case steel of other six factories, the larger size of inclusions in this sample is the main reason for the difference from other factory products. Through research,the unreasonable desulphurization process is the main reason for the cracking defects of the battery case steel. After optimizing the production process to pretreat the hot metal and direct casting after converter smelting, the product has no significant cracking problem.